1.3 6

• Gene mutation


  Permanent change in the DNA of an organism
• Protein synthesis


  The genetic code carried on the DNA is translated into living cellular material
• If a single codon is changed or misread during protein synthesis

  The amino acid for which it codes may be different, resulting in the whole polypeptide chain and final protein being altered
• Mutation


  A permanent change in the DNA of an organism
• Mutations can happen when the gametes (sex cells) form, or during the division of somatic (body) cells
• A tiny alteration at the molecular level may have no noticeable effect, or devastating effects on the whole organism
• Many human genetic diseases are the result of random mutations in the genetic material of the gametes
• Gene mutations


  Changes in the bases making up the codons
• The body has DNA repair systems that cut out or repair damaged parts of the DNA strands
• Point or gene mutations

  Mutations where just one or a small number of nucleotides are miscopied during transcription
• Substitution


  A type of point mutation where one base substitutes for another
• Deletion


  A type of point mutation where a base is completely lost in the sequence
• Insertion


  A type of point mutation where an extra base is added, which may be a repetition or a different base
• Chromosomal mutations


  Changes in the positions of genes within the chromosomes
• Whole-chromosome mutations


  The loss or duplication of a whole chromosome
• Down's syndrome is caused by a whole-chromosome mutation where individuals have three copies of chromosome 21 instead of the usual two
• Mutations can be a source of variation within an organism
• Very occasionally, a mutation occurs that results in the production of a new and superior protein, which may help the organism gain a reproductive advantage
• Most mutations are neutral, meaning they neither improve nor worsen the chances of survival
• Some mutations cause great damage, disrupting the biochemistry of the entire organism
• Sickle cell disease


  A genetic disease that affects the protein chains making up the haemoglobin in the red blood cells, caused by a point mutation
• Sickle cell disease


  1. A change of one base in one codon changes a single amino acid in a chain of 147 amino acids, altering the nature of the protein

  2. The haemoglobin molecules stick together to form rigid rods that give the red blood cells a sickle shape, preventing them from carrying oxygen efficiently and blocking the smallest blood vessels
• Mutations in the body cells can cause problems such as cancer
• The most damaging mutations occur in the gametes because they will be passed on to future offspring, giving rise to genetic diseases
• Exposure to mutagens, such as X-rays, ionising radiation and certain chemicals, increases the rate at which mutations occur
• Gametes


  Haploid sex cells produced by meiosis that fuse to form a new diploid cell (zygote) in sexual reproduction
• Point mutation (gene mutation)


  A change in one or a small number of nucleotides affecting a single gene
• Substitution


  A type of point mutation where one base in a gene is substituted for another
• Deletion


  A type of point mutation where a base is completely lost
• Insertion


  A type of point mutation where an extra base is added into a gene, which may be a repeat or a different base
• Chromosomal mutations


  Changes in the position of entire genes within a chromosome
• Whole-chromosome mutation


  The loss or duplication of a whole chromosome
• Sickle cell disease (sickle cell anaemia)


  A human genetic disease affecting the protein chains making up the haemoglobin in the red blood cells
• Mutagen


  Anything that increases the rate of mutation